gmc74

Last week I decided to see how my gas mileage would change with 91 octane over 87.

The first full tank of 91, here are the numbers-

420 miles on 17.2 gallons, or 24.41 mpg
All of these miles are with the A/C on high about half of these miles were city and half were highway, this is not my normal mileage breakdown. It is usually about 80% highway to 20% city.

Surprisingly, my on board computer said 24.5 mpg...

I am going to run a few more tanks of super, then a few tanks of regular to see if I notice a difference. I can't notice any difference in performance at this time.

bluemaxx

I can't tell any difference between 87 and 93. It isn't as hot in Dallas but we stay near 100 in July and August. The altitude here is +/- 430'. Maybe on the coast 87 would ping? I guess a couple of trips to the dyno would answer the question but...

2004SexMissile

I have consistently used premium (91) fuel and have gotten between 23 and 26 miles per gallon. While I typically spend anywhere from two-thirds to three-fourths of a tank solely on interstate commuting to work, I'm also forced to do a lot of in-town driving -- and compelled to rev the 3.5 up to 90-plus some as well -- so hitting the high-water mark of 28 mpg will probably never be in the cards unless I take a major road trip.

I have used regular octane fuel a couple of times, and have observed no drop-off in performance, however. It's probably not advisable to course 87 through your car's veins all the time, but I certainly can't imagine it creating any issues every once in a while.

gmc74

In one of the other threads I posted something about an article that I read, which basically said that if your car isn't knocking and pinging, the octane level is fine. I have used 87 every time from April until now and haven't had one knock or ping. I am testing out the improved mileage theory right now. I will be heading on a short roadtrip next weekend, so that should give me some definite highway numbers.

MONTE 01&97 SE

iTrader: (1)

Yeah and we have the high humidity unlike GMC in Arizona.

astil

iTrader: (1)

It must be nice if the car works with the 87 gas. I got a 99 GxE that doesn t run good at all w/87. Maybe Nissan fixed that problem...or maybe your knock sensors are too new at this point.Hope that nothing change there...

04maxima

With 4,000 miles, I have yet to see better than 22.8 mpg. I drive mostly interstate at about 65-75 mph..........of course there's normally some punk in a Grand Prix or Monte Carlo that Needs to be shown the supremacy of the '04...so well, then..............

04EliteSE

Since my first oil change, I have been getting better gas mileage... and I drive rather spiritedly... mid 20's up to as much as 27mpg according to actual figures, and not the trip computer.

bluemaxx

Your calculations show better results than the computer or worse?

04EliteSE

Sometimes better, sometimes worse, but not by much... one should keep in mind that the computer shows an average. Only by doing real math when you fill up can you tell what your mileage actually is.

zear0

havent seen better than 19mpg yet using 92 octane. car has 1200 miles on it. my average speed is around 35mph due to my horrid commute. i drive pretty softly about 80% of the time and drive aggressively maybe 2 - 3% of the time. did i screw it during the break in? i was pretty careful not to push it until i hit 1000 miles.

only caveat here is that the car had 500 miles on it when i took delivery. it was driven from buffalo to boston...

any ideas why my mileage sucks so bad?

thanks

04EliteSE

zear0, I wouldn't worry just yet when taking into consideration your 35mph average during most of your driving. That actually sounds about right under the circumstances...

gmc74

I averaged 23.8 MPG on my second full tank of 91.

I took the car to CA this weekend, I averaged 81 MPH on the way there, and 84 MPH on the way back based on mileage and time on the Trip computer. Damn those trucks going 40 in the mountains, I was above 90 most of the trip.

As you may have guessed, the gas mileage wasn't great. I got 22.8 going there and 22.7 on the way back. The first was with 91, the second with 87.

I really don't notice any difference between the two octanes, and the gas mileage is minimally different.